1. Field of the Invention
This invention relates to gas and oil production from wells and can be employed for exploitation of oil-bearing formations on a stage of natural flowing of the wells and also in case of artificially supplying of compressed air into the wells for lifting oil via air-gas lift method.
2. Prior Art
There are three possible structures of gas-liquid mixtures in production wells where lifting of oil to the surface is enabled by a gas:
1. An emulsion or foam structure, which is characterized by a more or less uniform distribution of gas in liquid. The gas is present in the liquid in a form of small bubbles (smaller than diameter of the lift tubing);
2. A beaded or slugged structure. In the case of such structures most of the gas moves in the form of bubbles filling the whole cross-section of a tube and alternating with slugs of liquid;
3. An axial or annular structure. In the case of such structures most of the gas moves along the tube axis as a continuous flow (gas blast) and the liquid moves along the walls in the form of a thin layer.
For vertical and inclined flows one can refer to a Hewitt chart of regimes of flowing (FIG. 1).
A method is known to form an emulsion structure of a gas-liquid flow in a lift column and devices to disperse gas into liquid (I. M. Muraviev and N. N. Repin, Research of Motion of Multicomponent Mixtures in Wells, Nedra, Moscow, 1972, pp.129-139).
Its shortcomings are:
from point of view of gas consumption the emulsion structure is not optimal;
devices to disperse gas into a liquid are mounted at the bottom end of the lift column where gas is injected into the liquid. However the gas bubbles coalesce while they move upward causing the flow structure to be destroyed, i.e. it is not possible to obtain a stable structure by this method;
creation of emulsion structure of a gas-liquid flow (especially if surface active substances are added) makes more difficult the subsequent separation of gas after the liquid (oil) has been lifted to surface.
A method is known to form a slugged regime of flowing in a gas-liquid mixture and devices therefor (Yu. V. Zaitsev et al., Theory and Practice of Gas Lift, Nedra, Moscow, 1987, pp. 67-71). This method is the closest to the proposed one in its technical essence. In specialized literature this method is known as a displacement lift and is realized as follows. At the lower end of the outer row of tubes in a two pipe lift column a displacement chamber is placed equipped with a reflux valve in which chamber a liquid is being accumulated, and after injecting into it of a gas the slug of the liquid is ejected into lift tubing and thus elevates. This process is periodically repeated. Variants of displacement lift can employ compressed gas cutoff either on a surface or bottomhole.
The main shortcomings of this prototype are:
it is possible to create a beaded (slugged) regime of a flow at the initial path of a lift column, but very soon it decays and becomes chaotic because the gas bubbles go into regime of floating up (drifting) and do not perform the useful work all along the whole lift column;
it is necessary to employ a two row lift column;
the devices controlling the lift are rather sophisticated;
high level of losses of compressed air;
lift production capacity by liquid is limited;
it can""t be used in free flowing wells.
A device is known for periodic gas lift to elevate the liquid from wells (Authorship Certificate, USSR no 1117395, 03.02.83) that comprises a tubing column and a replacement chamber comprising an overflow nipple with a flange rigidly placed in the tubing column and a turned over cup placed above the said nipple and forming together with the nipple a chamber being in its lower part hydraulically connected with inner space of the tubing pipes.
This device being the most relevant by technical solution is the closest one to the proposed invention. Main shortcoming of the said known device is that the displacement chamber is made from rigidly connected elements and therefore its volume available to form a gas slug is limited. It does not provide a possibility of self-adjusting of a system of gas-liquid slugs to variation of parameters of the gas-liquid mixture or hydrodynamics of a rock-well system.
Technical result of the invention is providing of a possibility of self-adjusting of a system of gas-liquid slugs to respond variations in parameters of the gas-liquid mixture or hydrodynamics in a xe2x80x9crock-wellxe2x80x9d system. This technical result is achieved due to transformation of a gas-liquid flow in wells due to sequential placement of devices separating gas and liquid phases with intervals providing condition qup greater than qdown, where qup is amount of liquid being elevated, and qdown is amount of liquid draining down. A device for transforming of a gas-liquid flow in a well comprises a tubing column and a displacement chamber which chamber is made in a form of a turned over cup and an overflow nipple placed in the tubing column which cup and nipple form a chamber hydraulically connected in its lower part with the inner space of the tubing pipes, and according to this invention said cup is admitted to move axially and its travel path is defined and regulated by the following condition:
F greater than Vg(xcfx81liqxe2x88x92xcfx81gas)xe2x88x92Gxe2x88x92Pstat,
where: F is a force rising the cup, V is a volume of gas in displacement chamber, G is the weight of the cup accounting for the fact that it is in liquid, Pstat is a hydrostatic pressure on the cup, g is a gravitational acceleration, xcfx81liq and xcfx81gas are densities of the liquid and gas, respectively.
The technical result can be also achieved in a device wherein the displacement chamber is made in a form of a cup having side openings in its lower part and a flange on the top which flange normally closes the gas outlet passes in a sleeve rigidly connected at the pipe joint of the tubing column, and said flange is admitted to move axially within said sleeve.